Gas turbine engine exhaust ejector nozzle  with de-swirl cascade

ABSTRACT

The exhaust ejector nozzle has a tubular wall defining an exhaust flow passage leading to an outlet plane, and a de-swirl cascade including a plurality of circumferentially interspaced fins each having a first end connected to the wall adjacent the outlet plane and a second end extending into the exhaust flow passage. The de-swirl cascade can maintain the pumping action of the ejector in high swirl exhaust conditions.

TECHNICAL FIELD

The application relates generally to exhaust ejectors of gas turbineengines and, more particularly, to handling residual swirl in theturbine exhaust.

BACKGROUND OF THE ART

Gas turbine exhaust ejectors typically consist of a high-velocityprimary flow that leaves a primary component, referred to as a nozzleand transmits momentum to the surrounding medium by shear forces,thereby entraining the surrounding medium into a secondary flow. Theprimary and secondary flows then proceed into a secondary componenthaving a larger diameter and referred to as a shroud. Typically, thenozzle is made integral to the engine, whereas the shroud is madeintegral to the aircraft.

The entrainment of secondary flow with such ejectors is sensitive toresidual swirl from the turbine exhaust. The residual swirl can beparticularly high at operating conditions such as ground idle androtor-locked (hotel mode) conditions, for instance. Beyond a certainthreshold of swirl angle, the pumping process of the ejector can becomeunsatisfactory. Known methods to address this concern remained notcompletely satisfactory from the efficiency, cost and/or weightperspective. Accordingly, there remains room for improvement inaddressing the ejector swirl.

SUMMARY

In one aspect, there is provided an exhaust ejector nozzle for a gasturbine engine, the exhaust ejector nozzle comprising a tubular wallhaving a radially inner surface delimiting an exhaust flow passageleading, along an exhaust flow direction, to an outlet plane of theexhaust ejector nozzle, the outlet plane being circumscribed by adownstream edge of the radially inner surface relative the exhaust flowdirection, the radially inner surface of the tubular wall defining acentral axis, the central axis and the radially inner surface beingassociated with an exhaust flow orientation; and a de-swirl cascadeincluding a plurality of circumferentially interspaced fins each havinga first end connected to the radially-inner surface of the tubular walladjacent the downstream edge and associated outlet plane, a second endextending into the exhaust flow passage along a given span, and a chordoriented normal to the span.

In a second aspect, there is provided a gas turbine engine comprising anejector having a nozzle and a cowl at an exhaust region, the nozzleextending from a turbine exhaust case of the gas turbine engine, theejector nozzle having a tubular wall defining an exhaust flow passageleading to an outlet plane, and a de-swirl cascade including a pluralityof circumferentially interspaced fins each having a first end connectedto the wall adjacent the outlet plane and a second end extending intothe exhaust flow passage.

In a third aspect, there is provided a method of de-swirling an externalportion of an exhaust gas flow in an ejector nozzle of a gas turbineengine prior to mixing with a secondary flow in an ejector action, themethod including exposing at least the external portion of the exhaustflow inside the ejector nozzle to a de-swirl cascade including aplurality of circumferentially interspaced fins; the exhaust flowreaching an outlet plane of the ejector nozzle subsequently to saidexposing.

Further details of these and other aspects of the present invention willbe apparent from the detailed description and figures included below.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures, in which:

FIG. 1 is a schematic cross-sectional view of an example of a gasturbine engine;

FIG. 2 is an oblique schematic view showing an ejector nozzle connectedto a turbine exhaust case;

FIG. 3 is an end view of the components of FIG. 2.

FIG. 4 is a side view of an alternate embodiment of an ejector nozzle.

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a turbine engine. In this example, theturbine engine 10 is a turboshaft engine generally comprising in serialflow communication, a multistage compressor 12 for pressurizing the air,a combustor 14 in which the compressed air is mixed with fuel andignited for generating an annular stream of hot combustion gases, and aturbine section 16 for extracting energy from the combustion gases. Theturbine engine terminates in an exhaust section.

In this example, the exhaust section includes an exhaust ejector 18which is used to draw an external flow of air for ventilation, cooling,or the like. The exhaust ejector 18 in this embodiment generallyincludes a nozzle 22 and a shroud 27. The nozzle 22 has a tubular wall26 which guides a flow of exhaust gasses exiting the turbine section 16.The exhaust gasses travelling through the nozzle 22 and subsequentlyexiting will be referred to in this specification as the primary flow 23which travels in a direction generally indicated by the arrow.Henceforth, an inlet plane 44 of the nozzle 22 can be defined as beingcircumscribed by a first edge 46 of the tubular wall 26, positionedupstream relative to the average flow direction of the primary flow 23.An outlet plane 48 can be defined as being generally circumscribed by asecond edge 50 of the tubular wall 26, positioned downstream relative toan average flow direction of the primary flow 23. The first edge 46 andsecond edge 50 can be circular, and can alternately be elliptical if thecorresponding plane is slanted, for instance.

The primary flow 23 can be annular around a center body 32 or circular,such as in alternate embodiments where the center body 32 is recessedfor instance. The exact average orientation of respective portions ofthe primary flow 23 will be affected by the configuration of the tubularwall 26, center body 32 as well as by other aerodynamic considerationsknown to those skilled in the art. The configuration of the exhaust flowpath of the primary flow 23 through the nozzle 22 is affected by theshape of the radially-inner surface 31 of the tubular wall 26. A centralaxis 29 can thus be defined relative the tubular wall 26. Areas locatednearer to the axis 29 can thus be referred to as being radially-inner,whereas areas located relatively farther to the axis are relativelyradially-outer. Accordingly, the tubular wall 26 can be said to have aradially-inner surface 31 (FIG. 2) exposed to the primary flow 23 and anopposite radially-outer surface, a portion of which may be exposed to aradially-outer surrounding medium.

During normal operation of the ejector 18, the energy from the velocityof the primary flow 23 of exhaust gasses entrains a surrounding,radially-outer, secondary flow 25 of the surrounding medium by shearfluid friction forces into a secondary component of the exhaust ejector18 referred to as the shroud 27, which has a larger inlet plane 52cross-sectional area than the cross-sectional area of the outlet plane48 of the nozzle 22 to allow for entry of both the primary flow 23 andthe secondary flow 25. The inlet plane 52 of the shroud 27 can thus besaid to radially exceed the inlet plane 48 of the nozzle 22.

FIGS. 2 and 3 show an example of an exhaust ejector nozzle 22. In thisembodiment, the nozzle 22 is provided as an individual component shownconnected to a turbine exhaust case 24, but it will be understood thatin an alternate embodiment, the nozzle 22 can be a portion or extensionof the turbine case itself, for instance. Further, referring to theillustrated embodiment, the exhaust nozzle 22 can be seen to have atubular wall 26, being here generally cylindrical, and a radially-innersurface 31 of the tubular wall 26 defines an exhaust flow passage. Thetubular wall 26 can be cambered, curved or bent to some extent dependingon the intended use, in which case the central axis 29 follows the curveor camber; further, one end or both ends of the tubular wall 26 can bebent or slanted off the radial orientation, for instance.

The nozzle inlet 28, which bears the upstream edge 46 of the tubularwall 26, is connected to the turbine exhaust case 24 in this case. Thetubular wall 26 also has an opposite outlet end 30 bearing thedownstream edge 50 of the tubular wall 26. In this embodiment, theoutlet end 30 is slanted, so the edge 50 of the tubular wall 26 iselliptical to some extent instead of being circular. An inlet plane 44can be defined as the entry into the nozzle 22 whereas an outlet plane48 can be defined as the exit, circumscribed by the downstream edge 50.In this embodiment, a centerbody 32 is shown connected to the turbinecasing 24 by struts at the inlet plane 44 of the nozzle. Although thepresence of the centerbody 32 and struts are typical, the shape,position, and configuration thereof can vary in alternate embodiments.Typically, the struts and fins are independent of each other. However,in some cases, the designer may want to clock the fins such that no wakefrom the struts is aligned with any of the fins.

Ejector pumping breakdown can result from high swirl angles in the shearlayer between the primary and secondary flows. The breakdown isexacerbated by possible hub separation and migration of the flow towardsthe shroud 27. The pumping breakdown is naturally to maintainconservation of angular momentum, with the separated flow near the hubsubstantially in a solid body rotation. A solution is to implement apartial cascade 34 before the nozzle exit plane 48 to reduce the swirlangle in the area where the pumping shear forces occur between theprimary and secondary flows.

To this end, in this embodiment, the exhaust nozzle 22 further comprisesa de-swirl cascade 34 including a plurality of circumferentiallyinterspaced fins 36 each having a first end 38 connected to the wall 26,and more particularly connected to the radially-inner surface 31 of thetubular wall 26, and a second end 40 extending into the exhaust flowpassage, in a direction which will be characterized here as beingradially-inward from the radially inner surface 31. It will be notedhere that the ducting is generally annular in shape and is positionedadjacent the outlet end 30 of the tubular wall 26.

To provide the ejector function, the primary flow 23 exiting the nozzle22 interacts with a surrounding medium to entrain a secondary flow intothe shroud 27. Referring to FIG. 3, the inner peripheral portion 60 ofthe primary flow 23 (schematically shown here delimited on the one handby an arbitrarily positioned dashed line and on the other hand by theinner surface 31 of the tubular wall 26) travelling inside the nozzle,i.e. the portion of the primary flow 23 which is adjacent theradially-inner surface 31 and in the inner periphery of the tubular wall26, will have a significantly greater effect in the ejector pumpingaction onto the surrounding medium, once it has passed through theoutlet plane 48 of the nozzle, than a more central, or radially-innerportion 42 of the primary flow 23. This is because although a certainamount of mixing can occur, at least a high percentage of the innerperipheral portion 60 of the primary flow 23 which travels close to theradially inner surface 31 of the tubular wall 26 near the outlet plane48 will remain in a radial position allowing it to interact with thesurrounding medium, which is located radially-outwardly. Theradially-inner portion 42 of the primary flow 23 which is located moreradially inwardly is separated from the surrounding medium by the innerperipheral portion 60 layer of the primary flow 23 and interactsindirectly with the surrounding medium if at all. Addressing the swirlin a radially inner region is thus less likely to produce an effect onthe ejector pumping action, just as partially addressing the swirl at anupstream position along the exhaust gas passage is less likely to beeffective because subsequent mixing of the exhaust gasses may allow anunsatisfactory amount of swirl to return into the portions of theexhaust gas flow which contribute to the ejector action.

Referring more particularly to FIG. 4, an annular critical region 62 ofthe exhaust flow passage in the nozzle is defined, being both adjacentthe outlet plane 48 and adjacent the radially-inner surface 31 (asillustrated by numeral 60 in FIG. 3). Strategically controlling theswirl in this specific region inside the nozzle may be more susceptibleto having a significant effect on the ejector pumping action than inregions located more radially inwardly or more upstream from the outletplane, and thus may be achieved at satisfactory added weight, pressure,and costs.

Even if high swirl is present across the entire cross-section of theexhaust gasses of the primary flow inside the nozzle, it can besatisfactory to control the swirl only partially, and strategically inthe inner peripheral portion 60 of the primary flow 23 and in theannular region 62 near the outlet plane 48. Rreferring back to FIG. 3,the fins 36 can extend only partially into the primary flow 23 in thedirection extending across the flow, radially-inward from the tubularwall 26, and can be positioned adjacent the outlet end 30 of the tubularwall 26, i.e. adjacent the outlet plane 48. This strategic positioningof the fins 36 connected to the tubular wall 26 of the nozzle 22 canstrategically control the swirl in high swirl conditions to preserve theejector pumping action with a limited amount of extra weight, pressureloss, and/or cost.

In the illustrated embodiment, the configuration of the de-swirl cascade34 is designed to reduce the swirl in the exhaust gases strategically inorder to maintain the ejector secondary flow pumping action even inconditions where there is a high degree of swirl in the exhaust gasses(such as a swirl angle of 40° or 50° for instance). The de-swirl cascade34, and more specifically the fins thereof, is positioned near thecritical region 62 of the ejector flow which eventually meets and shearswith the secondary flow into the pumping action.

In the illustrated embodiment, and referring to FIG. 4, in the directionof exhaust gas flow, the fins 36 have an upstream end 72 at a firstlongitudinal or axial position, and extend along their chord c (FIG. 4)to a downstream end 74. For practical purposes, the downstream end ofthe fins 36 can be separated from the outlet plane 48 by a spacingdistance d in this embodiment, but it will be understood that inalternate embodiments, the downstream end 74 of the fins can coincidewith the downstream edge of the radially-inner surface 31, i.e. theoutlet plane 48. If the distance d is too long, the deswirl actionthrough the fins will be partially lost as the high swirl near thecenter will migrate radially outwards, thereby favouring the breakdownof ejector pumping. In an alternate embodiment, the fins can beconnected to the nozzle inner wall surface 31 and protrude past theoutlet plane.

Because the region of the primary flow 23 which is responsible for thepumping action of the secondary flow 25 is more importantly the region60 thereof which is located adjacent to the wall, the fins 36 can bedesigned to extend only partially into the primary flow 23 area, in theinner-peripheral region 60, such as better seen in FIG. 3, to favour thelow-weight, low-pressure losses aspects. The span s of the fins 36 canrepresent only a fraction of the dimension of the primary flow area 42.In this specific case, they can be seen to extend through around lessthan half of the primary flow area 42 which can be delimited between thecenter body 32 and the radially-inner surface 31 for instance. Inalternate embodiments, the fins 36 can extend across the entire primaryflow area 42 and/or optionally be interconnected by a structural ring orcenterbody, for instance.

In the illustrated embodiment, an aim was to sufficiently control theswirl to maintain the ejector pumping action in high-swirl conditions,while optimizing weight and pressure losses added by the fins 36. Tothis end, the span I and chord c can be adjusted to minimum or optimumdimensions, and the fin count can also be adjusted to a minimum oroptimum value yielding results considered as satisfactory. The staggerangle can be close to zero, but can alternately be adjusted to maintainlow pressure losses. The fins 36 can be seen to extend more or lessnormal from the wall 26, radially inward, and have their chord parallelto the central axis 29, or alternately inclined therefrom by a staggerangle. The final adjustment of these design parameters will be typicallybe selected to achieve a trade-off between the ejector ability tofunction at both high swirl and aero design conditions (SFC), in whichthe swirl is typically low. Other design aspects are to be consideredsuch as structural integrity and manufacturability.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, the fins can be provided closer to nozzle inlet instead ofbeing adjacent the nozzle outlet, and the span, chord, fin count andstagger angle can vary. The de-swirl cascade can be applied to exhaustejector nozzles of any suitable turbine, such as turboshafts, turbopropsand APUs for instance. Still other modifications which fall within thescope of the present invention will be apparent to those skilled in theart, in light of a review of this disclosure, and such modifications areintended to fall within the scope of the appended claims.

What is claimed is:
 1. An exhaust ejector nozzle for a gas turbineengine, the exhaust ejector nozzle comprising a tubular wall having aradially inner surface delimiting an exhaust flow passage leading, alongan exhaust flow direction, to an outlet plane of the exhaust ejectornozzle, the outlet plane being circumscribed by a downstream edge of theradially inner surface relative the exhaust flow direction, the radiallyinner surface of the tubular wall defining a central axis, the centralaxis and the radially inner surface being associated with an exhaustflow orientation; and a de-swirl cascade including a plurality ofcircumferentially interspaced fins each having a first end connected tothe radially-inner surface of the tubular wall adjacent the downstreamedge and associated outlet plane, a second end extending into theexhaust flow passage along a given span, and a chord oriented normal tothe span.
 2. The ejector nozzle of claim 1 wherein the span of the finsextends only partially into the exhaust flow passage.
 3. The ejectornozzle of claim 2 wherein the span extends less than halfway into theprimary flow area.
 4. The ejector nozzle of claim 2 wherein the spanextends along an inner peripheral region of the exhaust flow passage. 5.The ejector nozzle of claim 1 wherein the chord is inclined by a staggerangle relative to the central axis.
 6. The ejector nozzle of claim 1wherein the span, the chord, the stagger angle, and an interspacingbetween the fins are selected to sustain a pumping action of the ejectorin high swirl conditions.
 7. The ejector nozzle of claim 1 wherein thefins extend normal to the radially-inner surface.
 8. The ejector nozzleof claim 1 wherein the second end of the fins is a free end.
 9. Theejector nozzle of claim 1 wherein the fins are immediately adjacent theoutlet plane.
 10. The ejector nozzle of claim 1 wherein the fins arespaced from the downstream edge by a spacing distance which is smallrelative to the span and the chord.
 11. The ejector nozzle of claim 1wherein the span and the chord are of the same order of magnitude. 12.The ejector nozzle of claim 1 wherein the tubular wall is cambered andthe central axis is correspondingly curved.
 13. A gas turbine enginecomprising an ejector having a nozzle and a cowl at an exhaust region,the nozzle extending from a turbine exhaust case of the gas turbineengine, the ejector nozzle having a tubular wall defining an exhaustflow passage leading to an outlet plane, and a de-swirl cascadeincluding a plurality of circumferentially interspaced fins each havinga first end connected to the wall adjacent the outlet plane and a secondend extending into the exhaust flow passage.
 14. The ejector nozzle ofclaim 13 wherein the fins extend partially into a primary flow area ofthe exhaust flow passage.
 15. The ejector nozzle of claim 14 wherein thefins extend less than halfway into the primary flow area.
 16. Theejector nozzle of claim 13 wherein the fins are oriented in an axialorientation relative the tubular wall.
 17. The ejector nozzle of claim13 wherein the free end of the fins extends normal to the wall.
 18. Theejector nozzle of claim 13 wherein the fins are immediately adjacent theoutlet plane.
 19. The ejector nozzle of claim 13 wherein the fins have aspan, chord, stagger angle, and interspacing selected to sustain apumping action of the ejector in high swirl conditions.
 20. A method ofde-swirling an external portion of an exhaust gas flow in an ejectornozzle of a gas turbine engine prior to mixing with a secondary flow inan ejector action, the method including exposing at least the externalportion of the exhaust flow inside the ejector nozzle to a de-swirlcascade including a plurality of circumferentially interspaced fins; theexhaust flow reaching an outlet plane of the ejector nozzle subsequentlyto said exposing.